The invention relates to a four-stroke reciprocating piston internal combustion engine having an exhaust gas turbocharger, and an operating method for such an internal combustion engine.
An internal combustion engine is known from DE 102 43 473 A1, having an exhaust gas turbocharger and multiple cylinders, each with a first and a second exhaust valve per cylinder, wherein the first and the second exhaust valves are combined to form in each case a separately controllable group. Exhaust gas from exhaust gas ducts associated with a particular group of exhaust valves may be supplied to separate inlets of a twin turbine of the exhaust gas turbocharger. At low speed only one group of valves is opened, and at higher speeds the exhaust valves of both groups are opened. There is a problem on the one hand in that the residual gas content in the cylinders is undesirably high when, at comparatively low speeds, a switch is already made to an operating mode in which all exhaust valves open. On the other hand, the thermodynamic efficiency of the engine is decreased when the speed limit of the switchover is shifted to higher speeds.
The object of the invention is to provide a generic internal combustion engine and an operating method for same in which the above-mentioned disadvantages are reduced.
The four-stroke reciprocating piston internal combustion engine according to the invention has an even number of cylinders, and an exhaust gas turbocharger with two turbine inlets which are at least substantially separate from one another. At least one intake duct, with an intake opening on the combustion chamber side, for intake of combustion air into a combustion chamber of the cylinder is associated with each of the cylinders. In addition, a first and second exhaust duct, provided for discharge of exhaust gas from the combustion chamber, are associated with each of the cylinders, the first exhaust duct having a first exhaust opening on the combustion chamber side, and the second exhaust duct having a second exhaust opening on the combustion chamber side. A first and a second exhaust valve are used for controlling the exhaust gas discharge from the combustion chamber via the first and second exhaust ducts by opening and closing the first and second exhaust openings. A first half of the cylinders is connected via a respective first exhaust duct to a first of the two turbine inlets, and is connected via a respective second exhaust duct to a second of the two turbine inlets. In addition, a second half of the cylinders is connected via a respective first exhaust duct to the second turbine inlet, and is connected via a respective second exhaust duct to the first turbine inlet. According to the invention, it is provided that the second exhaust openings have a larger diameter than the first exhaust openings. Accordingly, the diameters of the valve disk of the associated first and second valves are different. This difference in sizes of the valve disk diameters and exhaust opening diameters allows improved purging of residual gas. In addition, an increase in the speed limit, in which a switch is made from an operation with actuation of only one exhaust valve to an operation with actuation of both exhaust valves of each cylinder, is made possible without decreasing the thermodynamic efficiency of the engine.
To make the best possible use of the advantages, it is provided to select the second exhaust openings or the valve disk diameter of the second exhaust valves to be at least 10%, but preferably at least 15%, 20%, or even larger, than the diameter of the first exhaust opening or the valve disk diameter of the first exhaust valves.
The engine according to the invention is preferably designed as a 4-cylinder or 6-cylinder engine, in particular having an in-line design. The associated turbocharger may be a so-called twin scroll turbocharger or a segment turbocharger.
In one embodiment of the invention, a first intake duct having a first intake opening and a second intake duct having a second intake opening are provided for each cylinder. The engine is thus designed as a so-called 4-valve engine. In another embodiment of the invention, it is particularly advantageous when the second intake openings have a larger diameter than the first intake openings. Analogously to the second exhaust openings, the second intake openings may have a diameter that is selected to be at least 10%, but preferably at least 15%, 20%, or even larger, than the diameter of the first intake openings.
In another embodiment of the invention, particularly good, stable combustion is achievable when the first intake duct is designed as a swirl duct or turbulence duct, and the second intake duct is designed as a filling duct. Swirl or turbulence which stabilizes the combustion may thus be generated in the combustion chamber. To this end, the direction of the intake duct axes is suitably oriented with respect to the cylinder axis.
Furthermore, for a good charge cycle and an advantageous combustion process, in another embodiment of the invention it is provided that the second intake openings are situated diagonally opposite from the second exhaust openings in a view of the cylinders from the top.
In another embodiment of the invention, four cylinders, one through four, for the internal combustion engine are arranged in series, the first and fourth cylinders forming the first half of the cylinders and the second and third cylinders forming the second half of the cylinders, and a firing order of one-three-four-two being provided for the cylinders. A standard counting method for the cylinders, beginning with a side opposite from the power output of the engine, is to be assumed. With the stated firing order in conjunction with the differently sized exhaust openings, it is possible to achieve a particularly low transverse influence on the purging processes and a particularly low fraction of residual gas remaining in the cylinders.
The object underlying the invention is achieved with an internal combustion engine and by an operating method in which at low speeds below a predefined lower speed limit, the first or the second exhaust openings are kept closed by their associated exhaust valves. Above a predefinable upper speed limit, the internal combustion engine is operated in such a way that the two exhaust openings are opened for all cylinders by actuating the exhaust valves in the customary manner toward the end of the power stroke, and are closed once again shortly after top dead center of the exhaust stroke. In one embodiment of the method, it is provided that the lower speed limit, as a function of load, is predefined between approximately 15% and 50% of the nominal speed of the internal combustion engine.
In another embodiment of the method, in an internal combustion engine having two intake openings per cylinder, wherein the second intake openings have a larger diameter than the first intake openings, at low speeds below a predefined speed limit of the internal combustion engine the first intake openings having the smaller diameter are kept closed by their associated intake valves. This measure as well benefits the charge cycle.
Advantageous embodiments of the invention are illustrated in the drawings and described below. The features stated above and to be explained below may be used not only in the particular stated feature combination, but also in other combinations or alone without departing from the scope of the present invention.